USE OF WASTE & LOW VALUE CLAYS TO REMOVE METALS FROM POLLUTED STREAMS AND DISCHARGES
SUMMARY REPORT
Please note that the full report is available from Aquatonics, please email Dr Phil Smith at phil@aquatonics.com
AQUATONICS LTD
Glenthorne, Searle Street, Crediton, Devon, EX17 2DB, UK
Tel: 01363 776456 E-mail: phil@aquatonics.com
PHILIP R J SMITH, BSc, PhD, MCIWEM, MRSC, CChem.
28 MARCH 2003
CONTENTS
EXECUTIVE SUMMARY
INTRODUCTION
Metal Removal by Clays
Clays from Dredging
Impacts of Mining on Streams and Rivers in the UK
Treating Pollution from Mines and Spoil Heaps
Metals in Industrial Effluents
Other Contaminants
SUMMARY OF EXPERIMENTAL RESULTS
Data on Eling Clay
Eling Clay in Suspension
Comparison of Various Clays & Other Sediments
Trials of a Prototype at Wheal Jane Mine, Cornwall
Clay Beds
Packed Columns
Lignitic Clay used in a Permeable Reactive Barrier
Noodled Clays in Permeable Bags for Emergency Response to Spills
TECHNICAL AND LOGISTICAL ISSUES
Disposal of Contaminated Clay
Applications of Clay Technology
CASE STUDY: APPLICATION OF CLAY TECHNOLOGY TO THE RESTORATION OF DARLEY BROOK, CORNWALL
Constructed Wetlands
In-stream Treatment
Treatment with Clay in Suspension
ACKNOWLEDGEMENTS
REFERENCES
EXECUTIVE SUMMARY
This SMART feasibility study has shown that dredged clays and other clays with low economic value have considerable commercial potential for removing metals from effluents and contaminated streams. Novel methods of treating effluents and polluted streams have been devised, including "in-stream treatment" of watercourses which has many advantages over conventional treatment methods.
The most important findings are:
Although all clays and silts remove metals such as copper and zinc, there are significant differences between the clays, which we attribute to the cation exchange capacity of the clay and its ability to raise the pH of the test solution.
One of the best-performing clays that we tested was a glauconitic clay from Eling, in Southampton Water. This clay is very similar to the material that would be dredged from the Dibden area in Southampton Water if a proposed container terminal obtains planning permission.
A significant beneficial use could be found for clays from capital dredging. These clays are normally dumped at sea in the UK. This disposal method causes environmental problems at the dump site, for example smothering of marine life on the sea bed. Dredging companies in the UK are required by the licensing authorities to consider potential beneficial uses of the dredged material.
There are logistical and engineering problems to overcome before dredged clays could be used in large quantities. These problems are not technically difficult to solve, but would require investment by the dredging industry. Such investment is unlikely unless Government Agencies require dredging companies to stop dumping clays and silts at sea, as this is likely to remain the cheapest option.
Toxicity tests using one of the most sensitive species of freshwater invertebrate (a snail called Physa acuta) showed that a suspension containing 1% Eling clay (dry weight) had a dramatic effect on the toxicity of an actual mine water discharge. The Eling clay produced a reduction in toxicity that was equivalent to a 100 fold dilution with clean water. This indicates that some marine clays that would otherwise be dumped at sea may have a genuine role in cleaning up polluted streams and rivers, both in the UK and overseas.
Trials with industrial effluents from Printed Circuit Board Manufacturing and Metal Finishing showed that clays in suspension can remove 60-93% of copper from the final effluent, depending on the concentration of clay used. Other metals are also removed but not as efficiently as copper.
Laboratory trials using a recirculating system showed that a 4 metre flume lined with Eling clay could remove copper highly effectively, even at high concentrations (110 ppm Cu) without causing any problems with increased concentrations of suspended solids.
Eling clay beds and suspensions of Eling clay have a remarkable ability to neutralise acidic effluents. If such clays are used to treat acid mine drainage they are unlikely to require the addition of other neutralising agents such as limestone.
China clay and ball clay quarries often have low value clays stock-piled within their quarries, and many of these clays could be used to remove metals from solution. Lignitic clays from WBB Minerals are relatively acidic and have the ability to neutralise alkaline effluents. The combination of carbonaceous material and clay in these lignitic clays would be expected to increase the range of pollutants that could be removed.
There are hundreds of kilometres of streams in the UK that are affected by metal and coal mines (mostly ones that have closed). Most of these could be treated using clays, either in suspension of as clay beds within the stream (in-stream treatment). Unfortunately there is only slow progress in the UK, as the responsible agencies do not have sufficient funding. In addition the Environment Agency sees itself as an enforcer of water quality standards in England and Wales, rather than a body with responsibility for cleaning up streams. Responsibilities will hopefully be clarified and money from central government should be made available as the deadlines of the EU Water Framework Directive approach.
"In-stream treatment" of contaminated streams and rivers is a concept developed by Aquatonics Ltd. It appears to be a practical and economic alternative to the current methods, which involve either chemical treatment or constructed wetlands. In-stream treatment is predicted to be much cheaper in capital and operating costs than chemical treatment, but more expensive than constructed wetlands or clay lined lagoons.
Permeable Reactive Barriers (PRBs) using a combination of synthetic aggregate made from clay and raw clays have considerable potential for cleaning up groundwater contaminated with metals and other contaminants. The synthetic aggregate can be designed to provide the desired level of permeability.
Industries that could benefit from clay technology include: mining and quarrying, including active and abandoned mines radioactive facilities (eg nuclear power stations and Sellafield) oil refineries whisky distilleries (copper in effluent comes from the distillation vats) metal smelting metal finishing and other metal engineering works printed circuit board manufacturing leachates from landfill sewage treatment drinking water treatment In the light of current world events it is worth pointing out that clays could also be used to remove some nuclear and chemical contaminants from water following terrorist attacks on water supplies.
| Terms & Conditions | Copyright Aquatonics Ltd | Site Map |
